Polyurethane foams have long been recognized for their ability to act as an insulating material. These foams are prized due to their low density and relatively high insulating capability. As such, a number of products have used polyurethane foam as their primary means of insulation. One example of such a product is the refrigerator. During the manufacturing process, a fixed volume of foam is dispensed into the hollow refrigerator shell such that the cavity of the shell becomes filled with the expanded polyurethane foam, thereby creating an insulated food compartment.
The polyurethane foam itself is comprised of the reaction product of an isocyanate and a polyol, or blends thereof, which, upon contact, react to form the polyurethane foam. Accordingly, these foam precursor components are preferably contacted and mixed just prior to the time of application. In this way, foam is not formed from the precursor components prematurely, i.e., prior to the time the precursor components exit, or are on the verge of exiting, the dispenser.
As mentioned previously, the contact and mixing of the foam precursor components, and the resulting formation of the foam, should occur as close to the outlet of the dispenser as possible. Despite taking precautions in this regard, however, prematurely-formed foam can build up in the interior of the dispenser, clogging control valves and passageways such that the dispensing device is rendered inoperable.
As alluded to previously, one of the most difficult problems associated with these polyurethane dispensers is not the accurate metering of the various precursor components into a cavity, but cleaning the device after use. Despite the best efforts of designers to alleviate the problems of deposits forming on the interior surfaces of these devices, there remains troublesome solid deposits on valves, delivery lines, and other elements on these dispensing devices after only a relatively short period of use.
Various methods have been developed to remove these deposits from the interior of dispensing devices. Organic solvents, such as methylene chloride, have been used to clean polyurethane foam dispensers for years, these solvents being circulated through the interior of the dispensers after use. However, due to recent governmental regulations which restrict the disposal of these solvents, the industry has turned to other cleaners which do not contain these restricted components.
One example of a purportedly less environmentally harmful cleaner is Neutra-Flush III (Brulin & Company, Inc., Indianapolis, Ind.) which contains 1-5 percent sodium metasilicate. However, this cleaner also contains what is classified in the art as a solvent. In addition, this material, like other solvents, may cause irritation of the eyes and skin of the user. Moreover, the resulting polyurethane/solvent composition is also difficult to dispose of in view of present state and federal standards for waste disposal. However, permits for disposal of this cleaner are not as difficult to obtain as the aforementioned methylene chloride-based cleaners.
An alternative cleansing system is disclosed in U.S. Pat. No. 4,485,840. This patent provides a flushing system for a metered delivery apparatus, said apparatus being adapted for the delivery of an adhesive material. The adhesive material, which contains a water-dispersion polymer, such as a polyol, and polyisocyanate, may be flushed from the dispensing device (or gun) by use of this system. Generally, the system contemplates that warm water, which may include additions such as acids, bases or detergents, be circulated through those areas of the dispensing gun which contact the adhesive. Optionally, air may be delivered in short bursts to provide additional agitation for better cleaning action.
Further, a solvent cleaning fluid line is attached to the isocyanate delivery line of the gun, this solvent preferably being capable of solvating isocyanate. During cleaning, this solvent flows through the isocyanate delivery line and acts to remove the solid deposits derived from the isocyanate during use of the metering delivery system described previously.
In view of the limitations inherent in known polyurethane foam dispenser cleaning methods, a need exists for a solvent-free procedure which is non-toxic to humans, inexpensive, and relatively easy to dispose of after use.